|Author(s)||Prevosto Marc1, Van Iseghem Sylvie1, Moreau Benjamin1, Forristall George Z.2|
|Affiliation(s)||1 : Ifremer, Brest, France
2 : Shell Global Solutions U.S., USA
|Abstract||Despite its great theoretical and practical importance, the statistical distribution of crest heights has remained poorly known. The uncertainties are due to difficulties both with the theory, where nonlinear effects must be accurately modeled, and with measurements, where different sensors appear to give different results. In response to this uncertainty, the Wave Crest Sensor Intercomparison Study (WACSIS) was formed as a Joint Industry Project in order to provide data for comparing the response of wave sensors and for comparing theories of crest height distributions with the measurements.
The key to the WACSIS experiment was to place all of the popular sensors on the same platform located where they were likely to experience large waves in one season. The location of the measurements was in shallow water because the nonlinearities that produce extreme wave crests are stronger in shallow water. Measurements in shallow water thus give better tests of both instruments and theories. The project was set up on the Meetpost Noordwijk (MPN) measurement platform. The platform is a piled steel jacket structure in 18 meters deep water, located 9 kilometers off the Dutch coast near the coastal resort of Noordwijk, whence it got its name. The platform is one of the stations of the North Sea Monitoring Network ('Meetnet Noordzee', MNZ), that gathers on-line hydrological and meteorological information from the North Sea. A complete description of the project is given by van Unen et al. (1998).
WACSIS was very successful in collecting a nearly complete data set from all of the instruments during the winter of 1997-98. The second phase of the WACSIS project focused on the interpretation of the wave data. Many aspects of wave statistics have been studied, but the main emphasis has been on crest height distributions, and recommendations for crest heights to be used in air gap calculations. This report will describe, first the different steps which have been followed to construct a common data base from the raw data collected at the Meetpost Noordwijk measurement platform, secondly various analyses of the data base in term of crest height-period joint distributions, intercomparison of the crest measurements by the sensors and comparisons with numerical second order irregular wave models. Finally, new models of crest distribution will be proposed and compared with other state of the art models.
Ref. van Unen, R.F., van Beuzekom, A.A., Forristall, G.Z., Mathisen, J.-P., Starke, J., 1998, "Wacsis - wave crest sensor intercomparison study at the Meetpost Noordwijk measurement platform", Proc. Oceans Conf.
Prevosto Marc, Van Iseghem Sylvie, Moreau Benjamin, Forristall George Z. (2001). WACSIS, Wave Crest Sensor Intercomparaison Study : Common Data Base, Analyses, Crest Height Models. TMSI/IDM/COM/00-040. https://archimer.ifremer.fr/doc/00117/22841/